1. Field of the Invention
The present invention relates to methods for metal substrate treatment. More particularly, the present invention relates to methods for treatment of metal substrates with compositions comprising Mannich-derivatized polyethers. These methods provide improved corrosion resistance and/or paint adhesion properties to the metal substrate being treated.
2. Background Information
The present invention is directed to methods which are generally useful in the art of metal substrate treatment, particularly the treatment of phosphatized metal substrates, and more particularly the post-treatment of phosphatized metal substrates. Such treatment imparts improved corrosion resistance to the substrate, and improves the adhesion of final coating layers such as paints, inks, lacquers and plastics. The need for applying protective coatings to metal substrates for improved corrosion resistance and/or paint adhesion characteristics is well known in the art of metal finishing, as well as other metal arts. The usual technique for applying such protective coatings to metal substrates involves contacting a clean metal substrate with a solution containing phosphate and possibly other metal ions to form a corrosion resistant, nonreactive phosphate complex coating on the metal substrate. Because such coatings convert the metal substrate from a chemically active surface readily susceptible to oxidation to one having improved corrosion resistance and/or paint adhesion properties, they are known in the art as "conversion coatings".
The corrosion resistance and paint adhesion of conversion coatings can be further enhanced by treating the metal substrate with a post-treatment solution. Typical of such solutions are dilute aqueous acidic solutions containing a hexavalent chromium compound. Because of the toxic nature of hexavalent chromium compounds, however, expensive treatments must be used to remove chromates from effluent water to prevent the pollution of rivers, streams, drinking water sources, etc. Therefore, although chromium post-treatment solutions and processes are known to be effective, recent development efforts have been directed to discovering alternatives to chromium-containing compounds for post-treatment of conversion coatings.
U.S. Pat. No. 4,376,000 discloses processes for post-treating a phosphate-type conversion coated metal surface comprising contacting the surface with polyvinylphenol or its derivatives. U.S. Pat. Nos. 4,433,015 and 4,517,028 disclose aqueous compositions comprising polyvinylphenol and polyalkenylphenol derivatives and acid salts thereof, respectively; processes for treating a metal surface comprising contacting said surface with these aqueous compositions are also disclosed. U.S. Pat. No. 4,457,790 claims an aqueous solution comprising a metal ion and a polyvinylphenol derivative or acid salt thereof. A process for treating a metal surface comprising contacting said surface with the aqueous solution is also disclosed.
U.S. Pat. No. 5,523,363 relates to a resin obtained by reacting an epoxy resin, an amino compound and a phenol compound, and an epoxidized novolac-substituted phenolic resin. The resin is useful as an aqueous coating, particularly for cationic electrocoatings. There is no teaching of polymerizing the components, or of using the resin to treat metal or polymeric surfaces.
U.S. Pat. No. 5,298,289 discloses processes for treating certain plastic or painted surfaces with liquid surface treatment comprising water and a water soluble or dispersible polyphenol polymer which contains substituted aminomethyl groups on some of the phenyl rings of the polyphenol. Other polyphenol compounds useful in metal treatment are disclosed in U.S. Pat. Nos. 5,116,912, 5,039,770 and 5,266,410 and EPO 319 016.
U.S. Pat. No. 5,324,347 relates to a composition comprising a liquid solvent or dispersant or surface coating composition and a 2,6-bis(substituted aminomethyl)phenol. There is no teaching that the phenol be polymerized with an epoxy.
U.S. Pat. Nos. 5,389,405, 5,412,011 and 5,451,431 disclose aqueous solutions for coating a metal surface comprising a polymer, a silicate and an organofunctional silane. Methods of coating a metal surface comprising contacting said surface with the aqueous solutions are also disclosed.
WO 93/09265 discloses a treatment for the formation of a corrosion resistant film on metal surfaces. This treatment includes use of a phosphate surface-treatment bath containing a cationic organic polymeric compound having at least one cationic nitrogen atom. Disclosed as one of the polymeric compounds is the adduct of HN(CH.sub.3).sub.2 with a bisphenol A epoxy resin.
European Patent Application 639,627 discloses aqueous solutions for pre-treating a metal surface, particularly aluminum, consisting essentially of an anionic polyacrylamide copolymer. A method of coating a metal surface which comprises contacting said surface with any of the aqueous solutions is also disclosed. Uses of other acrylate-containing compositions in treating aluminum are disclosed in U.S. Pat. Nos. 4,191,596 and 5,122,202.
U.S. Pat. No. 3,994,989 discloses a paint binder comprising the reaction product of a Mannich base and an epoxide resin containing at least one 1,2-epoxide group. U.S. Pat. No. 4,001,155 similarly discloses a paint binder for the cathodic electrocoating of electrically conductive metal surfaces comprising the reaction product of a Mannich base and an epoxide resin containing 1,2 epoxide groups. U.S. Pat. No. 4,396,732 discloses the Mannich base of an amine resin prepared by reacting a dihydric phenolic compound with a diepoxide. None of these reference, however, disclose the use of such resins as a sealing rinse in the treatment of metal or polymeric surfaces.
Mannich condensates of a substituted phenol and an alkylamine containing internal alkoxy groups are disclosed in European Patent Application 469,203.
There remains a very real and substantial need for chrome-free methods for treating various metal substrates, particularly phosphatized metal surfaces. The present invention addresses this need.